Process control involves the use of instruments, control devices and systems for measuring and manipulating control elements such as valves to maintain one or more process variables, such as temperature, pressure and flow at target values selected to achieve a desired objective of a process including the safe and efficient operation of machines and equipment utilized in the process. Process control systems have widespread application in the automation of industrial processes such as those used in chemical, petroleum, and manufacturing industries, for example.
Control of the process is often implemented using microprocessor based controllers or computers which monitor the process by sending and receiving commands and data to hardware devices to control a particular aspect of the process or the entire process as a whole. The specific process control functions implemented by software programs in these microprocessors or computers may be individually designed, modified or changed through programming without requiring modifications to the hardware. For example, an engineer might cause a program to be written to have the controller read a fluid level in a tank (from a level sensor), compare the tank level with a predetermined desired level, and then open or close a feed valve based on whether the read level was lower or higher than the predetermined, desired level. The parameters may be changed easily by displaying an engineer's view of the process and then by modifying the program using the engineer's view.
In addition to carrying out the execution of control processes, software programs are also used to provide feedback in the form of an operator's display or view regarding the status of particular processes, to signal an alarm when a problem occurs, or to provide instructions or suggestions to an operator when a problem occurs. The operator who is responsible for the control process needs to view the process from his point of view. A display or console is typically provided as the interface between the microprocessor based controller or computer performing the process control function and the operator and also between the programmer or engineer and the microprocessor based controller or computer performing the process control function.
Systems that perform, monitor, control, and feed back functions in process control environments are typically implemented by software written in high-level computer programming languages such as Basic, Fortran or C and executed on a computer or controller. These high-level languages, although effective for process control programming, are not usually used or understood by process engineers, maintenance engineers, control engineers, operators and supervisors. Higher level graphical display languages have been developed for such personnel, such as continuous function block and ladder logic. Thus each of the engineers, maintenance personnel, operators, lab personnel and the like, require a graphical view of the elements of the process control system that enables them to view the system in terms relevant to their responsibilities.
For example, a process control program may be written in Fortran to require two inputs, calculate the average of the inputs and produce an output value equal to the average of the two inputs. This program could be termed the AVERAGE function and may be invoked and referenced through a graphical display for the control engineers. A typical graphical display may consist of a rectangular block having two inputs, one output, and a label designating the block as AVERAGE. A different program may be used to create a graphical representation of this same function for an operator to view the average value. Before the system is delivered to the customer, these software programs are placed into a library of predefined user selectable features. The programs are identified by function blocks. A user may then invoke a function and select the predefined graphical representations to create different views for the operator, engineer, etc. by selecting one of a plurality of function blocks from the library for use in defining a process control solution rather than having to develop a completely new program in Fortran, for example.
A group of standardized functions, each designated by an associated function block, may be stored in a control library. A designer equipped with such a library can design process control solutions by interconnecting, on a computer display screen, various functions or elements selected with the function blocks to perform particular tasks. The microprocessor or computer associates each of the functions or elements defined by the function blocks with predefined templates stored in the library and relates each of the program functions or elements to each other according to the interconnections desired by the designer. Ideally, a designer could design an entire process control program using graphical views of predefined functions without ever writing one line of code in Fortran or other high-level programming language.
One problem associated with the use of graphical views for process control programming is that existing systems allow only the equipment manufacturer, not a user of this equipment, to create his own control functions, along with associated graphical views, or modify the predefined functions within the provided library.
Thus, new process control functions are designed primarily by companies who sell design systems and not by the end users who may have a particular need for a function that is not a part of the standard set of functions supplied by the company. The standardized functions are contained within a control library furnished with the system to the end user. The end user must either utilize existing functions supplied with the design environment or rely on the company supplying the design environment to develop any desired particular customized function for them. If the designer is asked to modify the parameters of the engineer's view, then all other views using those parameters have to be rewritten and modified accordingly because the function program and view programs are often developed independently and are not part of an integrated development environment. Clearly, such procedure is very cumbersome, expensive, and time-consuming.
What is needed is a uniform or universal design environment that can easily be used, not only by a designer or manufacturer but also a user, to customize an existing solution to meet his specific needs for developing process control functions. Such a design environment would enable a process control designer or user to modify a standard process control function or create a unique customized process control function and create the graphical views to be associated with the modified or newly created process control function, all within a common environment. The design environment should have a common interface for both the creation of the function and for its associated engineers, operators, lab and maintenance personnel or other desired users such that when the engineer's function is modified or created, the modification or creation manifests itself in all other graphical views of the function. In addition, the design environment should have a common database structure of attributes and methods and the graphics associated with the process control function to allow modified or created process control functions to be represented in whatever graphical methodology that is desired or required by the designer, whether by ladder logic, continuous function block or other design languages required by the various engineer, operator, lab, and maintenance personnel as other desired graphical views.